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A Journal of VHF-UHF Radio Technology <S Engineering 
Published at 

COMMtronics Engineering - PO Box 262478 - San Diego, CA 92196 
Publisher/Editor: Bill Cheek a.k.a. f *Doctor Rigormortis" 
Administrator: Cindy Cheek a.k.a. “Sunbunny" 

Copyright © 1991-95 <AU rights reserx*J> ISSN 1861-9240 
Volume 5 Number 8 $5.00 

some very legitimate needs to know 
what’s going on in situations where it’s 
ill advised to have others privy to your 

Amplifier through a rotary switch so as 
to afford the capability of listening to key 
areas around your perimeter. Power can 
be fed by a cheap DC Adapter. 



~ The Saga Continues ~ 

A reader recently complained about our 
SuperSnoop series, wondering what the 
hell it had to do with scanning. Well, 
this month’s installment should yield a 
clue or two. Think about it. 

First, we presented the SuperSnoop 
microphone, so sensitive, it’s capable of 
detecting the heavy breathing of a couple 
of gnats making w hoopee at a distance of 
73 yards. But what’s so hot about a 
super sensitive microphone without an 
amplifier to boost the weak signals to 
speaker-playback volume? 

So, last month, I laid on you the 
SuperSnoop Amplifier. Together, the 
SuperSnoop Microphone & SuperSnoop 
Amplifier are a very potent dynamic duo 
that stand on their own merits. 

But what about times when you are 
persona non-grata and need or want to 
listen in on what’s going on? The 
presence of your magnificent personage 
can be distracting to the goings-on, but if 
you could be remotely located and still 
hear, then so much the better, right? 

Take you parents, fer instance. You 
might use a baby monitor to keep tabs on 
Junior and Queenie as they sleep. When 
they get older, the baby monitor can be 
moved to the rumpus room so you can 
keep tabs on how much blood is being 
drawn at any given time. 

Trouble monitors are never as 

good as they’re cracked up to be. They 
don’t sound all that good for one tiling. 
The units are large and bulky and cannot 
be operated from batteries. They’re 
definitely not portable, nor very well 
suited for clandestine and treacherous 
situations. Baby monitors do not make 
very good bugs for a variety of reasons. 

Not that I am advocating the fine arts 
and sciences of surreptitious bugging; I 
most assuredly am not! But there are 

Take fer instance that peephole in your 
front door. It’s nice to know what’s 
going on outside your door before you 
open it. It’s nice to know what’s going 
on all around your property before you 
jump into the middle of something with 
both feet. But peepholes aren’t always 
available, and neither do they serve the 
purpose in all instances. 

My SuperSnoop series can add an 
immense measure of security to your 
home and family. In many instances, 
just the microphone and amplifier will 
suffice. You could embed several 
Microphones out of sight around your 
property; feed their outputs into the 

But wired listening devices are not 
always suited to given situations. 
Sometimes, radio is ideal, and that’s 
where this month’s SuperSnoop 
Transmitter and a scanner enter the 
picture. The output of the SuperSnoop 
Amplifier can be fed to the input of the 
SuperSnoop Transmitter for a superb. 
high quality radio listening device! 

Do NOT mistake my words here....we 
are talking quality\ I’m sure a lot of you 
guys have experimented with Radio 
Shack’s listening device, #33-1076, the 
FM Wireless Mic. Cute, but no cigar. 
Poor range and low sensitivity. Eats 
batteries, too. 



|l. The crystal isn't critical, but probably shouldn't be lower 
than 10 MHz, nor higher than 50 MHz. Synthesizer crystals 

in the 22-38 MHz range from old CB radios work great! 

2. An optimum value may be as high as 1100-ohms. Use 

a 2-k trimpot to determine best value. 

3. An optimum value may be as low as 4000 ohms. Use 
a 100-k trimpot to determine best value. 

4. Ground traces and connections are shown in 
heavy black lines. All grounds are interconnected. 

5. RF choke should be 220-uH to 470-uH or so. 1-mHok. 

6. Varactor diode is critical, but try the common 

ECG/NTE 613, 614, 617, 618 first. See text. ,- 

+ 9 volts 



Audio In 

• Ground 

4n ^ 


^: Note 3 




2N2222A, etc 

Note 4 \ 

■ Ground 

Antenna, 10" 

- Ground 

12/6/95 ~ 9:02 PM ~ Page 1 

Make no bones about it, my SuperSnoop 
Transmitter will knock your socks off 
when you hear its quality. There is no 
doubt in my mind this little puppy will 
equal or exceed the quality of pro-snoop 
devices! It’s unbelievable! But true! 


First. I gave you the Microphone. It’s 
eminently useful as a stand-alone device, 
say with tape recorders or as a feed to an 
amplifier. Now just in case you didn’t 
have an amplifier handy, I gave you the 
SuperSnoop Amplifier to take up the 
slack. Now, we add the transmitter, for 
one whopper of a listening device when 
remote operations are needed. I have 
been spoonfeeding you a system! 

But we’re not ready for the system yet. 
The Microphone was a stand-alone 
project, as was the Amplifier. So, too, is 
the transmitter! Never mind this month 
that the Microphone and Amplifier can 
drive the Transmitter. This month, the 
general idea is as another stand-alone 

Next month. I will wrap it up for you 
into a single, unitary system project. 
This month, we just focus on the Super 
Snoop Transmitter for whatever purpose 
and use you can find for it. And there 
are several, not including any audio 


If you need just an oscillator , as many 
scannists do. in order to test your 
receiving systems with a low-power 
signal, the Transmitter is just right for 
you. If you don't need audio transmitting 
capability, then using the schematic on 
page 1, amend it as shown: 

You'll note we eliminated the varactor 
diode, RF choke: two 10-k resistors: and 

a bit of wiring. In a word, the basic 
Transmitter is super easy to build, and if 
you need to transmit high quality audio, 
the required “extras” are not a big deal. 
The rest of this project will deal with the 
Transmitter as if audio were needed, but 
you needn’t get hung up on that, if all 
you need is a source of RF with which to 
test your receivers. In that case, build 
the circuit as shown on this page, and 
use a small trimmer capacitor by which 
to precisely adjust the frequency if 
needed. You can just ground that end of 
the crystal, too, and dispense with the 
trimmer capacitor, as shown by the 
dotted line, if you don’t need precision 
tweaking capability. 


Our transmitter is just a basic cry stal 
oscillator, garden variety, nothing 
special. In fact, it’s so unspecial that it’s 
slicker than snake snot smeared on ice. 
High quality oscillators put out only one 
frequency. Ours puts out a bunch of 
frequencies. More on that later. 

The heart-throb of the Transmitter is, of 
course, the quartz crystal, and it’s not 
critical aside from maybe two tilings: 

(1) Frequency should not be higher than 
about 40-50 MHz, nor lower than about 
8 MHz. You’ll see why in a minute. 
And (2), the crystal should be of the 3 rd 
Overtone type, though really, most any 
“rock” will do. The neat thing about 
overtone crystals is that you can salvage 
‘em from junked synthesizer-type CB 
radios. Any CB shop will have hundreds 
of synthesizer crystals on hand, one of 
which shouldn’t cost much. 

The ideal crystal for this project is one 
with a fundamental operating frequency 7 
in the 37 MHz band, of which there are 
six very common cuts available from 
junked CB rigs: 

JsBP T i 

There are many other useful values of 
crystals that can be found in junked CB 
radios, so there is no need to run out and 
buy sometliing special. Other useful CB 
synthesizer crystals are in the ranges of 
23 MHz, 41 MHz, 16 MHz, & 11 MHz. 

Overtone synthesizer crystals are 
optimum for this Transmitter because 
they allow oscillations, not only at the 
fundamental frequency of the crystal, but 
also at each of at least the first eight 

harmonics of the fundamental. This 
usually unsavory characteristic is what 
lets us use a variety of crystals, down to 8 
MHz or so. (Harmonics are multiples of 
the fundamental.) 

Let’s suppose you used a crystal with a 
fundamental of 11.500 MHz. The useful 
harmonics would be: 23.0, 34.5, 46.0, 
57.5, 69.0, 80.5, and 92.0 MHz, or even 
higher. That’s right, the oscillator will 
generate all these frequencies and maybe 
even more. So wliile the fundamental 
and 2 nd harmonic frequencies are not 
covered by most scanners, the 3 rd and 
higher harmonics are....and when your 
scanner is tuned to one, there will be no 
doubt in your confused mind that you’re 
getting a signal. It won’t take long for 
you to learn how to use those signals to 
test and evaluate your scanners. And if 
you feed the Transmitter with a source of 
audio, it will act a lot like a baby 


If the crystal is the heart of an oscillator, 
then the varactor diode (or trimmer 
capacitor) is the brain and nervous 
system. Now if all you want is a 
transmitter (without audio), then forget 
the varactor diode and just use a trimmer 
capacitor as shown on this page. Or, 
don’t use one, if precision adjustment of 
frequency is not necessary. With the left 
side of the crystal grounded as shown by 
the dotted line, the crystal will use its 
internal capacitance to set a resonant 
frequency (and harmonics). An external 
capacitor simply allows precision setting 
of the resonant frequency. It’s up to you. 

The Varactor Diode is the most critical 
component if you want a high quality 
audio transmitter. Varactors are basically 
silicon diodes, but made in a special 
manner that makes them act like variable 
capacitors when reverse biased. The 
amount of capacitance varies according 
to the level of the reverse bias voltage. 
By the way, all silicon diodes exhibit a 
varactor effect to some degree, but only 
“real” varactors can be used for our 
purpose. And even then, not just any 
varactor will do, though you can 
experiment cheaply enough. 

Before I get into the SuperWhizBang 
type of varactor that you really want, 
let’s take a quick look at what can be 
used for the sake of experimenting. You 
might never have heard of varactor 

12/6/95 ~ 9:02 PM~ The “WorldScanner Report” © 1991-95; Volume 5, No 8; Page 2 

ECG/NTE Varactor Tuning Diodes 




VR = 4 V. 1*1 MHz 


C2/C30 Q 1 = 1 MHz 






Vr * 4 Vdc. 1 * 50 MHz 


















































NTE or 



F tnnnl 
CarrvrA If 



Ftgun of 













FM Tuning 



100 ®3 V 

34 (min) ® 3 V 

2.5 min 


AM Tuning 




ISO 0 1 V 

440 (min) @ 1 V 


tuning diodes, but they are as common as 
fleas on a junkyard dog. Go to your local 
semiconductor supply house and buy one 
each of the following ECG or NTE part 
numbers: the cost is modest. 

613 614 617 618 

One of these may work quite well, and if 
so, your search will be neither lengthy 
nor costly. I can’t attest to these 
varactors because I use a more costly 
commercial version that I’ll tell you 
about in a minute. To my way of 
thinking, if the above work, then let’s 
use the KISS principle. NTE/ECG 
suppliers are everywhere. Sources for 
my special varactor diodes are few and 
far between. The above are common and 

The chart at the top of this column offers 
clues on what varactor diodes do and 
how they function. In a word, they act 
like the “trimmer capacitor” shown on 
the previous page. The capacitance 
varies with the reverse bias placed on the 
diode. ( Varactor diodes are never 
forward biased....that is, we do not want 
them to conduct!) 

Instead, we want to send an audio (AC) 
voltage to the varactor in such a manner 
that its reverse bias changes at the audio 
rate. When this happens, the output 
frequency of the oscillator will also 
change at the same rate. Voile! FM! 
Frequency Modulation - for clear, noise- 
free signals that can be readily received 
by common scanner receivers! 

Note the trimmer capacitor used in the 
drawing on the previous page? As said 
before, a varactor acts like a trimmer 
capacitor, except that you adjust it by 
changing the reverse bias voltage on the 
diode. Now understand that crystals 
“like” to be grounded, but happily 

tolerate some capacitance in the ground 
side. The more capacitance, the better, 
though. Too little, and the crystal will 
not oscillate. Therefore, we can’t use 
just any trimmer capacitor nor just any 
varactor diode. Either one must have a 
certain minimum capacitance, so our job 
is to select something that will not cause 
any problems with oscillation. It just so 
happens that 20-pF or more capacitance 
is usually sufficient to stabilize a crystal 
oscillator. Looking at the above chart, 
we see where ECG/NTE 610-612 fall 
under this mark, so we won’t consider 
them for our transmitter. However, 613, 
614, 617, and 618 look pretty good. 

Another important tiling about varactor 
diodes is the tuning ratio. A very 
narrow change of capacitance relative to 
the reverse bias means a small tuning 
ratio. This may not be sufficient to 
frequency modulate the transmitter. So 
we want a fairly large tuning ratio, as 
well. Diodes 613, 614, and 617 have 
tuning ratios of 2.5 to 3.0, while 618 has 
a whopper 15. Were it not for the “AM 
Tuning” spec. I’d say go for 618. As it 
is, the large 440-pF capacitance coupled 
with the AM-spec might render this one 
unsuitable for our needs. Try it, 
Otherwise, my gut feel for a workable 
varactor diode is the 617. One of the 
four might yield satisfactory results. 

Hyper-abrupt Tuning Diodes 

As mentioned earlier, I use a special type 
of varactor tuning diode called Hyper- 
Abrupt. Forgive me for not explaining it 
in detail, but space begs and it gets kind 
of complicated. Suffice it to say that this 
diode yields performance par excellence ! 
That’s why I prefer the KV1503 from 
Frequency Sources. The MV1401 or 
ZC807 from MSI Electronics should also 
work equally well, though I have not 

tried those from MSI. But before you go 
to these commercial suppliers, there is 
one other source for the superb kind of 
diode I am talking about. 

You die-hard CB’ers and Freebandcrs 
will know of a special tuning diode used 
to extend the range of SSB clarifiers or 
“sliders”. Once upon a time, known as 
the “M-15 diode”, “Super Slider Diode". 
“Super Tune Diode” and a variety of 
oilier colloquial names, these special 
diodes will serve the purpose in our 
SuperSnoop Transmitter. So check your 
CB/hack resources for one of these 
diodes, if need be. Otherwise, contact: 

Frequency Sources KV-1503 diode 

16 Maple Road 
Chelmsford, MA 01824 
(617) 256-8101 Fax (617) 256-8227 
MSI Electronics MV-1401 diode 

34-32 57 th Street ZC807 diode 

Woodside, NY 11377 
(718) 672-6500 Fax (718) 397-0972 

You should expect to pay an arm and a 
leg from the above sources, but maybe 
prices have dropped since I last 
purchased. If you run into a roadblock 
finding just the right diode, I have a 
small quantity of the KV-1503 and 
equivalents that I can let go for just a leg. 
See the end of this article for what I can 


Don’t let these puppies intimidate you. 
I’ve explained everything you need to 
know about varactor tuning diodes. Just 
hook the sucker up right, if you expect it 

to work.which means the anode is 

grounded and the cathode (banded end) 
goes to the crystal. 


An audio signal of several volts is fed to 
the oscillator as shown on page 1. The 
audio readily passes through the RF 
choke to the cathode of the varactor 
where it can change the capacitance as 
discussed. The RF choke isolates the RF 
crystal signal from the audio circuit, 
however, and is very important! A 
minimum of 220-uH is required, with 
470-uH or even 1-mH being just fine. 
We do not want RF leaking back into the 
audio circuits. Chokes block RF. 

Notice the two 10-k resistors, Ra & Rb l 
The top of Ra goes to the +9v DC source 
while the bottom of Rb is grounded. 
This means that 4.5-v is dropped across 

12/6/95- 9.14 FM~ The “World Scanner Report" © 1991-95; Volume 5 , No 8; Page 3 

each resistor, placing a +4.5v bias on the 
cathode of the varactor diode. But 
cathodes need a negative voltage to make 
the diode conduct! This is what I mean 
by reverse bias. It prevents the diode 
from conducting, even with audio signals 
as high as 9-v, peak-to-peak. 

If you don’t understand this hocus-pocus, 
don't worry.....just build the circuit as 
shown and do not change or deviate from 
the Ra/Rb/RF Choke circuit as shown. 


Everything else is fairly standard and 
needs no special discussion here. The 
transistor is not critical, but should be 
rated for operation up to 100 MHz or so. 
The 2N3904 or 2N2222A are known to 
work quite well in the Transmitter. 

The 4.7kQ (Note 3) and 3300 (Note 2) 
resistors can be somewhat critical with 
respect to the output power of the 
oscillator. If you want to optimize or 
peak this power, then start your design 
with a 100-kQ trimpot in place of the 
4.7kO resistor and a 2kO trimpot in 
place of the 330Q resistor. Preset them 
to 4.7kO and 3300 respectively, and 
later, you can adjust them for maximum 
signal strength at a remote receiver. 
Then replace the trimpots with fixed 
resistors of the values measured after the 


The SuperSnoop Trans¬ 
mitter requires several 
volts of audio signal on 
the cathode of the 
varactor diode in order 
to adequately FM- 
modulate the oscillator. 
By and large, the “loudness” of FM 
modulated signals is dependent on how 
much the input signal deviates the RF 
carrier. Varactor diodes are not known 
for permitting wide deviations, hence the 
probable need for a special diode. But 
even so, the modulating signal (audio) 
must be a full 1-volt or more to get any 
“loudness” in the transmitter output. 
Low level signals like those straight from 
a microphone will not adequately 
modulate the oscillator. 

Range of the Transmitter is extremely 
variable, depending on how you build 
and adjust the unit, as well as how high 
and long the antenna. Under ideal 
conditions with the Transmitter mounted 

on the roof of my house and a 20" 
antenna. I was able to listen to sounds 
around my property quite effectively over 
about a 1-block radius, using just a 
handheld scanner. Bear in mind that 
range is not always a desirable 
commodity. You don’t want the rest of 
the world monitoring your “personal 
bugs’, do you? Length and positioning 
of the antenna is a big determinant of 
range. You will want to experiment. 

The SuperSnoop Transmitter is designed 
for DC power from +9v. I suppose you 
could use somewhat higher or lower 
voltages with no ill effect, but don’t stray 
too far from specification. 

VARACTOR DIODES of the hyper-abrupt 
type are not commonly available, but can be 
purchased from COMMtronics Engineering 
for $15.00 ppd. See Reference Information 
at the top of page 1 for contact information. 
Try the cheaper ECG/NTE 617 or 618 
varactor diodes first, though. 


You didn’t think we’d 
fail to issue a caveat 
or two, did you? The 
biggest one is that of 
bugging, which is 
probably illegal as 
hell. My SuperSnoop 
Transmitter and related projects are not 
presented with the idea of your using 
them as “bugs”, though if miniaturized 
and concealed, they might well make 
better bugs than what the pro’s use. 
Instead, these projects are specified to be 
for testing and evaluating your scanners, 
and perhaps for use as high quality baby 
monitors, peripheral property monitors, 
and legitimate tilings like that. If you 
are into doing bugs, do them at your own 
risk with the under-standing that if 
you’re caught, you could face 
incarceration and/or stiff fines. 

The device could also be illegal in the 
sense of violating FCC rules. Normally, 
it should not be if the input power is kept 
under 100-mW and if the antenna is kept 
short to 10" or less. Still, I am not a 
lawyer and I can’t tell you what is legal 
or illegal. You and your attorney (or a 
judge and jury will have to determine 
that unique aspect. I just warned you 
that this puppy could be illegal 
depending on how and where it is used. 
Use common sense and discretion with 
these devices to keep out of the slammer. 


Next month, we will tie all three 
SuperSnoop circuits together into one 
powerhouse of a wicked little device. 
Meanwhile, I urge you to build and test 
these circuits independently as separate 
devices. The practice of building the 
separate devices for their separate uses 
will pave the way for my integrated 
system to come next month. You can 
then connect them together for an idea of 
what my total system will be like. But 
for now, each circuit can have unique 
little uses as independent devices. 

Like the Transmitter, for instance. You 
can use it as a “repeater” by feeding the 
audio from a radio, hi-fi, or base scanner 
into the input. Then, as you work in the 
yard or around the house, just carry a 
handheld scanner strapped to your waist 
with an earphone to enjoy your program 
source while you’re on the move. 

FOR THE PRO-2004/5/6 

ED NOTE: This is a rehash of and take- 
off from a similar article in V5N2. 

Over the years, I have seen a number of 
memory retention problems associated 
with these fine scanners. You may as 
well know something about the circuit 
and how it works. Troubleshooting and 
repair are relatively easy if you know 
what to look for and how to test the 
components. The circuits are simple and 
the components are few. 

Memory retention circuits are required 
for these scanners because they use Static 
Random Access Memory (SRAM) chips. 
Lesser scanners use EEPROM memory 
chips or on-board EEPROM inside the 
CPU chip. Actually, EEPROM is the hot 
memory chip these days because it 
requires no battery or other parts to 
preserve memory. The side effect is that 
EEPROM chips can’t hold a lot of data 
yet, and they’re expensive. Megamemory 
scanners still use SRAM that requires a 
constant voltage for “keep alive”. 

This “keep alive” voltage has to be 
present at all times, whether the scanner 
in ON or OFF and whether it is 
connected to power or not. The method 
by which this is accomplished is reliable, 
effective, simple, and inexpensive. 

This discussion will use the PRO-2006 
as a model, but the circuits for the PRO- 

12/6/95-9.02 p\f~ The “World Scanner Report" © 1991-95; Volume 5 , No 8; Page 4 

• 2004 and 2005 arc all the same. The 
circuits for the PRO-2035 and 2042 are 
not the same, but are close enough that 
this discussion may suffice for them, 
too. The text of this article uses circuit 
symbols for the PRO-2006, so don’t get 

Memory retention circuits for these 
scanners consists of a few well placed 
and selected components: 


Switching diode 

Current limiter resistors 

CMOS voltage regulator 

Filter capacitors for voltage regulator 

Switching transistor 

Noise filter capacitors 

Now for a quick explanation of how the 
Memory Retention circuit works. 

PRELIMINARY: Whenever the PRO- 
2004/5/6 scanners are plugged into AC 
or DC power, they are never fully turned 
off, even if the switch is off. See the 
below sketch of a typical power supply : 

It can be seen how either an AC feed or 
an external DC supply will provide 
power to the memory circuits even if the 
scanner is turned off. Therefore, the 
only circuits of critical concern are those 
with the purpose of retaining memory 
when there is neither AC nor DC power 
connected to the scanner. The large 
schematic at the top of this page shows 
how it is done in the PRO-2004/5/6. 

Whenever AC or DC power is connected 
to the scanner, Q33 produces and feeds 
about +9.2v through D56 to R-247, a 
current limiter for CMOS regulator,. 
IC9. Obviously, this +9.2v is regulated 
to +5v and fed to the CPU and SRAM. 

Now let’s back up to the cathodes of D56 
and D59. The +9v from the Memory 
Battery feeds through D59 to meet the 
+9.2v through D56, right? Well, 
theoretically, yes. In actuality, no. Take 
a closer look. If +9.2v from Q33 is 
present on the cathodes of D56 and D59, 
and if +9v is on the anode of D59, then 
D59 cannot possibly conduct because it 
is reverse biased ! Well, when D59 
cannot conduct, then the faucet for the 
Memory Battery is effectively turned off! 


Main Receiver Board CN-3 I Logic/CPU : 

fn Board 





+5v from IC-8 

CPU +5v 

The battery will sit there forever under 
that circumstance, doing absolutely 
nothing, all the while Q33 produces 
power for the CPU. 

Remember, Q33 produces +9.2 volts any 
time and all the time the scanner is 
powered, either by AC or DC, no matter 
whether the scanner is on or off. 

The story takes a turn when AC or DC 
power is lost or removed from the 
scanner. Q33 goes dead with no power\ 
IC9 would then fail to provide power to 
the CPU, except for the simple diode 
logic of D59 and D56! When Q33 goes 
dead, D56/D59 cathodes drop to 0-v. 
Cool, because the battery’s +9v is on the 
anode of D59. D59, therefore, becomes 
forward biased (the faucet opens) and 
allows battery power to pass to R247 and 
IC9, which don’t care where power 
comes from! The CPU and SRAM draw 
very little current in their “sleep” states, 
and so the battery can maintain memory 
for months, if need be. 

the above diagram. The key thing is at 
the base of Q29 where a voltage is 
applied from IC8, the scanner’s normal 
+5v regulator. IC8 turns on and off as 
the scanner is turned on and off. 
Therefore the base of Q29 has either +5v 
or Ov, depending. Q29 cannot conduct 
when the base is Ov and always conducts 
when the base is at +5v. 

When Q29 is off or not conducting, and 
when memory power is available from 
IC9, then the voltage at the collector of 
Q29 through R236 is +5v. This +5v is 
passed to the CPU HOLD function via 
CN3, Pin 9. When Q29 is on or 
conducting, then the voltage at its 
collector drops to Ov, and is passed to the 
CPU HOLD function in the same 
fashion. Therefore, a “low” or 0-v to the 
CPU HOLD pin tells it all is well and to 
kick into high gear. Conversely, a “high” 
or +5v on the HOLD pin tells the CPU to 
drop into a deep sleep to conserve 
memory and power. 

“Sleep” states? Well, yes, the CPU has 
one to preserve it’s internal memory 
when there is no external power. It 
needs only a little squirt of memory 
battery power to stay ever at the ready 
when power is reapplied. 

This “sleep” state is triggered by the 
HOLD signal that’s generated by Q29 in 

The HOLD signal clearly varies with the 
status of the scanner and whether it is 
turned on or off. In a word, the CPU 
drops into “deep sleep” when the scanner 
is turned off, and when there is no power 
to the scanner. Memory is preserved in 
the CPU and SRAM so long as IC9 
provides +5v to the CPU and SRAM. 

12/6/95 ~ 9.30 pm ~ The ''World Scanner Report" © 1991-95; Volume 5 , No 8; Page 5 

This article is not complete without a 
brief explanation of IC9. a very special 
type of +5v regulator. The S-81250HG 
is based on a CMOS design with the 
intent of consuming almost no extra 
current for itself. Otherwise, it is a lot 
like the more common 78L05 regulator 
that does the same thing, except with an 
overhead of 3 mA. That’s right, the 
78L05 draws 3-mA of current for itself, 
in addition to whatever is drawn by the 
load. That 3-mA would drain a 9-v 
batten' in a week, whereas the pA drain 
by the CPU and SRAM and almost no 
overhead drain by IC9 can feed from the 
batten for months, perhaps even years. 


This article is long overdue. The subject 
comes up all the time over the networks 
and around the grapevines. Listen up, 
you portable scannists: I’m fixing to lay 
the good words on you from the good 
book on Care and Feeding of the NiCd 
Batteries In Your Handheld Scanners. 

First how about some easily chewed and 
swallowed brass tacks facts ? 

1. NiCd batteries do not have the legendary 
“ memory ejfecf\ This myth was disproved 
by a NASA study over ten years ago. 
Forget it. Follow these “rules”, instead. 

2. A NiCd cell is fully charged at 1.44 volts. 
Any more than that and it could become 
damaged. A safe maximum recharge point 
is 1.40 volts per cell. 

3. The ( nominal ) half-charge level of a NiCd 
cell is 1.20 to 1.25 volts per cell. This is 
the usually published rating. Its only 
meaning is “half’ or median charge. 

4. A NiCd cell is considered to be fully 
discharged at 1.0 volts. It could become 
damaged if discharged below that level. 

5. The maximum safe recharge rate of a 
NiCd cell is V 3 of its ampere-hour (A/li) 
rating or milliampere-hour (mA/li) rating. 
(This is the fast charge C3 rate) 

6 . The safe trickle (maintenance) recharge 
rate of a NiCd cell is '/io of its ampere- 
hour rating. (A/h or mA/h). (This is the 
trickle or maintenance charge CIO rate. ) 

7. NiCd cells may be damaged or destroyed 
by excessive heat, defined as more than 
mildly warm to the touch. Cold will 
usually not harm a NiCd cell, but it should 
not be operated below freezing. 

8 . NiCd cells can self-discharge at a rate of 
up to 1% per day. Periodically recharge 
stored NiCd cells. 

9. It is a good idea to periodically discharge 
seldom used NiCd cells to 1.0-v per cell 
followed by an immediate full recharge. 

10. NiCd cells fare better under cycles of full 
discharge-full recharge than partial 

11. Periodically check the voltage of each 
cell in a pack after it has been fully 
recharged. Any cell that differs by 10% or 
more from the rest, is probably in the 
process of failure. When one cell goes, 
others soon follow. Replace dead or weak 
cells to preserve the lives of the rest! 

12. Manufacturer-specified rechargers do not 
always fully recharge their NiCd packs. 
You should check your recharger as 
described in this article to ensure that it is 
optimized for your seamier. If not, take 
remedial measures. 

13. If you use NiCd cells that differ from 
specification in the scanner manual, you 
will either need a different recharger or to 
modify the recharge circuit in the seamier. 
For instance, if you use Radio Shack’s Hi- 
Capacity™ “AA” cells (#23-149) or 
nickel-metal-hydroxide cells in lieu of 
Radio Shack’s Standard Rechargeable 
NiCds (#23-125) in RS scanners, the 
standard recharger will not provide a full 
charge. This defeats the purpose of 
costlier lii-performance cells. 

14. A NiCd pack can only recharge up to a 
value that’s equal to the recharger 
terminal voltage less the sum of all voltage 
drops in the recharge circuit. If the 
resultant voltage is less than 1.40v per 
cell, then the pack cannot fully recharge. 

Ok, this about sums up what it takes to 
care for and feed your NiCd powered 
handheld scanners. In general, the 
above rules apply to all NiCds, no matter 
where they’re used, but this article 
focuses on the unique needs of NiCd 
cells as used in handheld scanners. 

The above drawing accurately depicts the 
recharge circuit used in most handheld 
scanners: There may be minor 

differences from one scanner to the next, 
but they are not substantial. 

The illustration also shows simplified 
versions of that circuit so you can see it 
as it counts, even if you don’t read 
schematics very well. It is important that 
you understand the circuit so that you 
can take remedial measures as needed by 
your particular scanner! 

A scanner’s recharge circuit is really two 
circuits in one, when you consider that it 
has to recharge by one path and 
discharge or power the scanner by 
another. The key ingredient here is the 
51 pitched RECHARGE JACK. 






+ NiCd 

R «iof 


_ Pack 

When the recharger plug is inserted into 
this jack, it moves contact #2 so that it 
can’t touch contact #3. The (-) center 
lug of the plug connects with contact #1, 
while the (+) shell of the plug connects 
to contact #3. 

This has the effect of piping the 
recharger’s output direct to the Power 
Jack and the rest of the scanner, and 
through RL to the NiCd battery pack. In 
a word, the recharger can power the 
scanner and recharge the battery at the 
same time. Not recommended, though] 

Meat *n taters : The recharge path is 
through DL & LI into the battery, and 
out through L2 and RL. Simply stated, 
the recharge current goes through DL, 
LI, L2 and RL, and drops a voltage 
across each of these components! Take 
note, because this is important. 

Now consider that LI and L2 are chokes 
or coils, and that their resistance is 
probably well below 1 -Cl, so we can 
discount their effect on the circuit. LI 
and L2 are there to block sharp voltage 
spikes from entering the battery, but not 
to affect the recharge action. That leaves 
RL and DL to evaluate, and these are 
very important considerations to the 
proper recharging of your NiCd pack. 

No matter the output of the recharger, 
diode DL drops 0.6-volt off the top. RL 
drops an additional voltage equal to the 
current flow through it, multiplied by its 
resistance. Suppose the NiCd pack is 
fully charged and is drawing a trickle 
charge (Rule 6) of 45-mA. 

12/6/95 - 9:02 PM- The “WorldScanner Report” © 1991-95; Volume 5, No 8; Page 6 

If RL is 22Q, then the volts dropped 
across RL = 0.045 x 22 or 1 volt. Add 
the RL-drop to the 0.6v DL-drop for a 
total drop of 1.6v. Now suppose the 
NiCd pack has 6-cells. Rule 2 says 1.40 
x 6 = 8.40 volts. In order for the NiCds 
to receive a FULL charge, the recharger 
better put out 8.40 volts plus the sum of 
all drops (1.60v): exactly 10 volts\ Any 
less, and the NiCds will never fully 
charge. Any more, and they could be 
damaged or have a shortened life span. 

Now don’t get excited if there is a tenth 
of a volt difference, one way or the other. 
That small difference is not a concern. If 
more , however, there could be trouble. 

What if your recharger is not up to par? 
Well, you can usually fix it, but not like 
you’d think. For one thing, the actual 
recharger is probably ok. It’s the 
recharge circuit in the scanner that needs 
the fixing. But first, let’s lay the 
groundwork for how to be absolutely 
certain of the quality of your recharger 
and recharge circuits 

It all begins with a thorough 
understanding of The Rules given on the 
previous page. Even if you don’t 
understand them, you must abide them! 

The first step to assess the quality of your 
recharger system is to start with a new 
set of NiCd cells. If you test with an old 
set, that can’t accept a full charge of 
1.40-1.44v per cell, you really won’t 
know if the recharger is faulty, or if the 
cells are just too old and decrepit. You 
can perform the simple test on a old set 
of NiCds, and if they test up to a full 

charge, then well and good Older cells 
usually do not fully recharge, though, so 
it’s best to start with a new set. 

1. Charge or recharge a new NiCd pack 
for at least 18-hrs to ensure that it has 
charged all that it’s going to. 

2. Remove the NiCd pack from the 
scanner or charger and immediately 
measure and record its terminal 
voltage without anything connected to 
it. Ideally, it will show 1.40v to 1.44v 
per cell. (A 6-cell pack should be 8.4 
to 8.6 volts.) If so, all is well; you can 
stop here. If not, a remedy is strongly 
suggested. Here’s how: 

3. Measure and record the voltage of the 
recharger without it connected to 
anything. This is called “open 
circuit” or “ no-load voltage ”. {See K 
in the above drawing.) 

4. Connect the recharger back to the 
freshly charged NiCd pack, and again 
measure and record the voltage of the 
recharger. The voltage will be less 
than the no-load measurement. This 
is called “ voltage under load'. {See Y. 
in the above drawing.) 

5. Use the milliammeter function of your 
meter to measure and record the 
current flow. {See A in the above 
drawing.) The current flow into a 
fully charged NiCd pack should not 
exceed one-tenth the mA/h rating of 
the pack when fully charged. 

NOTE: Most handheld scanners use 
“AA” cells, which can have mA/li 
ratings of 450 to 1000 mA/h, depending 
on the brand and type of cell. Current 
flow should be 45-mA for 450 mA/h 

cells and 100-mA for 1000 mA/h cells. I 
have seen “AA” NiCd cells in 450. 600. 
650, 800, and 850 mA/li capacities. 
Nickel-metal-hydride “AA” cells can go 
to 1000-mA/h. 

We have two important considerations 
here: (1) the terminal voltage of a fully 
charged pack must not exceed 1.44v per 
cell, nor be appreciably less than 1.40v 
per cell, and (2) the safe maintenance or 
trickle charge for a fully charged pack 
should be equal to x /\ 0 the mA/li rating 
(CIO) of the pack. {The ”C” rating of 
one cell is the rating of the entire pack.) 

If the full charge pack voltage does not 
meet spec per Step 2, then chances are 
the charge current measured in Step 5 is 
too low (less than the CIO rating). The 
remedy for this is to increase the current 
just enough to meet the CIO rating but 
not to exceed it. To do this, the series 
limiter resistor (RL) in the scanner needs 
o be dropped to a lower value. So how to 
calculate it? 

6. First, understand that the present 
NiCd pack voltage + the diode drop 
{0.6v) + the RL drop {current x 
resistance) = the recharger loaded 
output voltage. 

12/6/95-9.02 pm ~ The “World Scanner Report” © 1991-95; Volume 5, No 8; Page 7 


V5NQS j 



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US FUNDS PAYABLE TO: COMMtronic* Engineering 



The only thing we can alter to change 
the pack voltage is the resistor. So we 
calculate a new value of RL as follows: 

RL = Edrop + Inow where E^p is the 
voltage dropped across RL and I flow is the 
current through RL. To do this, we need 
to know a few other things first. Lets 
collect those items that we do know for a 
fact. (1) desired pack voltage, (2) 
desired current flow, (3) loaded output 
voltage of the recharger. Let’s work 
with a practical example. Suppose the 
recharger undercharges a 600-ma/H pack 
with 48-ma when the pack is fully 
charged to 8.32 volts. 

We want: 

Desired pack voltage = 8.40v-8.60v 
Desired trickle charge = 60-ma 

We have: 

Loaded recharger output = 10.5 volts 
Resistor RL = 33Q 
Trickle charge = 48-ma 
Fully charged cell pack = 8.32 volts 

We calculate: 

Edrop Iflow * RL 

Edrop = 48-ma x 33Q = 1,58 volts 

Totaldrop Ldrop I^ldrop 

Totaldrop = 1.58v + 0.6v = 2.18 volts 

Net Volts to Pack = 10.5 - 2.18 = 8.32v 

Yup, so far, so good. Everything checks 
out to be reasonable. So now we need to 
replace RL with a lower value to allow 
an Inow of 60-ma. We do this by 
selecting a final full recharge voltage for 
the pack....let’s be conservative and 
choose 8.50 volts....halfway between 8.4 
and 8.6 volts. First, we assume that the 
recharger loaded output voltage won’t 

change and will remain at 10.5-volts. 
Now follow my logic here: 

If the recharger output is 10.5v and we 
want 8.5 volts (E Fina i) to the cell pack, 
then the sum of all drops must be 2.0 
volts. The diode DL will always drop 
0.60 volts so that leaves 1.40-volts for 
RL. We want a trickle charge (I no w ) of 
60-ma, so now we can calculate a new 
value of RL: 

RLftew — (Edrop) ~ (Iflow) 

RL New = (1.40-v) -s- (0.060-amp) 

RLncw = 23.30 

Cool! Just happens that 22Q is a common 
resistor value. Replace the 33Q RL in 
your scanner with a 220 resistor, and 
your NiCd pack should stabilize at a 
higher voltage, closer to the ideal max! 

There you have it....all the tools to ensure 
the health and good feeding of your 
NiCd batteries. Do understand the 
foregoing is not an exacting science; 
rather it is an iterative process where 
trial and error lead to the optimum 
design for your particular scanner. If 
you have more than one scanner, the 
results will probably differ for each! But 
now you understand why manufacturers 
do things the way they do....keeps things 
simple...and mediocre. 


Anonymous bv Request: Phoenix, AZ 
Hi Bill & Cindy: I need one of those PerCon CD- 
ROMs, so here's my attempt. 

My favorite gripe on our hobby is the press and 
their coverage and sometimes lack of coverage on 
our hobby. (The various rags that have some 
scanner coverage or only scanner coverage, I 

don't read the others) They all seem to make 
huge attempt to stay away from stories that are 
even a little controversial. (Read Interesting I 
have not seen one mention anywhere of Laura 
Quarantiello's two-facing of our hobby in "Police" 
Magazine. Only on the Internet Newsgroups 
could you find these types of stories. This only 
backs up your position of computers and our 
hobby, you must own one! I think these rags 
could make better attempts to cover different 
subjects each month. If you read one, you've read 
them all. Even the tech articles in some seem to 
be sometimes almost the same from one to the 
next. I won’t ramble on, you get the idea, most of 
these magazines are all the same. I enjoy the WSR 
a great deal. The almost totally technical format is 
exactly what I like. Thanks © 


But we’ll be catching up. Apologies to all those who 
have been inconvenienced by the delays. A 
combination of health problems and an overload of 
work conspired to put us beliind. Not to worry, every 
subscription is guaranteed to receive the proper 
number of issues. There are two more to go for the 
1995 calendar year, and we’ll be working overtime to 
get them out, hopefully this month. Do NOT be 
concerned by the expiration date on your mail label if 
it says “11/30/95”..’ll still receive all issues. 


I don’t know where to begin.....Let’s start with the 
Internet. We are now represented on the World Wide 
Web with a “home page ” and an FTP site\ 

Our WWW page address is exactly as follows: 

Our FTP site can be reached with an FTP client 
program or Unix shell account exactly as follows 
cts. com/usr/spool/ftp/pub/bcheek 

If your WWW Browser supports FTP, the address is: 
f tp: //f tp. cts . com/pub/bcheek 

I’ll tell you more next issue, but for now check out 
these sites and let us know what needs improvement. 

Mark my words, the Information Age has dawned! 

12/6/95-9:57PM- The “WorldScanner Report” © 1991-95; Volume 5, No 8; Page 8 

COMMtronics Engineering 
“World Scanner Report” 
PO Box 262478 

, > San Diego, CA 92196-2478 





F Super Snoop Transmitter - The Saga Continues! 
f Information on Frequency Sources, Inc. & MSI Electronics, Inc. 

F Memory Retention Circuits of PRO-2004/5/6 Explained 
+ Care & Feeding of NiCd Cells in Handheld Scanners 
+ Another Pet Peeve Winner Announced! 

F We’re Late and Behind - but Catching Up. 

+ What’s New? We’re on the Internet - Big Time / 

WWW: http: / /ourworld. CompuServe. com/homepages /bcheek 

FTP Client Site: cts. com/usr/spool/f tp/pub/bcheek 
FTP WWW Browser Site: ftp: / /ftp. cts. com/pub/bcheek